Process of making organic esters of cellulose



weaker acetic acid of fr Patented July 4, 1933 IEIERBEET E. MARTIN,JAMES or DELAWARE v Pnocnss or MAKING onea N0 Drawing. 7 Applicationfiled April 21,

This invention relates to the preparation of organic esters ofcellulose, particularly cellulose acetate, by a process that is not onlymore expeditious than the prior processes but also produces a superiorproduct. I

An object of our invention is to provide a process for theesterification and particularly the acetylation of cellulose, whichprocess shortens the period of time required for making such organicesters of cellulose.

Other objects of our invention will appear in the following detaileddescription.

It has been proposed to pretreat cellulosic material by various methodsfor rendering the same more reactive to esterifying agent-s, wherebycellulose esters of superior properties may be formed. iVe have foundthat if a cellulosic material is both pretreated and prehydrolized, thecellulosic material may be esterified rapidly, and cellulose esters ofsuperior properties are formed.

In accordance with our invention, we pretreat a cellulosic material,then prehydrolize the same, and then esterify the pretreated andprehydrolized cellulosic material.

The cellulos ic material that is to be treated in accordance with ourinvention may be any suitable cellulosic material commonly employed formaking cellulose esters. Examples of such cellulosic material arecotton, cotton linters, purified wood pulp, reconstituted cellulose,etc.

The pretreatment process comprises the treatment of the cellulosicmaterial with a suitable proportion of a lower fatty acid such as formicacid or aceticacid or with a mineral acid such as hydrochloric acid. Theformic or acetic acid may be app-lied to the cellulosic material in anysuitable manner, either in the form of a liquid, or in the form of avapor. One mode of pretreatment comprises the agitation of thecellulosic material with a relatively small amount of glacial aceticacid in a suitable apparatus, say a horizontal type of agitator. Insteadof glacial acetic acid, om 50% to strength may be used.

Instead of employing the organic acid in the liquid state, pretreatmentmay be effected W. ELDER, AND LINEVOOD N. ROGER-S, 0F CUMBERLAND,IMARYLAND, A$SIGNORS T0 CELANESE CORPORATION OIE AMERICA, A CORPORATIONto 30 parts of the glacial N10 ESTE-RS OF CELLULOSE 1328. Serial No.271,975.

by subjecting the cellulosic material to the vapors of the acid, such asacetic acid, formic acid or hydrochloric acid, the vapors being employedeither alone or in admixture with an inert gaseous carrier, such as air,nitrogen, carbon dioxide, etc, or the vapors may be generated by soakingthe cellulosic materials in concentrated or dilute acids andsubsequently passing air or other inert gas through t treatment, air orother inert through the materials in order arid wholly or partially.

The temperature of the pretreatment may be boiling temperatures of theorganic acid used, or it may be below such temperature, and may beordinary temperature or even below ordinary temperature. The time oftreatment may be varied from one hour to live hours or more, dependingon the concentration, amount, and nature of the organic acid used, andthe temperature employed. The amount of the lower fatty acid used may bevaried within wide limits, but we have found that if glacial acetic acidis used, ex cellent results are obtained by employing 10 acetic acid togas is passed to remove the parts of the cellulose.

After the cellulosic material has been subjected to a pretreatmentprocess, it is then given a prehydrolysis treatment. This prehydrolysiscomprises subjecting the cellulosic material to a bath containing theliquids normally used for esterifying cellulose, but which bath containslittle or no catalysts for promoting the esterification, so thatpractically no esterification takes place. During this prehydrolysistreatment, an

water that may material is destroyed, and probably the cellulose ishydrolized to some extent. The mixture of cellulosic material andprehydrolysis bath is stirred for a while and then a small amount ofalkaline material or alkaline salts of weak acids, e. g. sodium acetate,may be added to neutralize all or part of the trace of acid catalystthat is present, and the mass is then further stirred. As stated, theprehydrolysis bath contains a mixture of liquids such as are used for 1ematerials. Preferably after prebe contained in the cellulosicesterifying cellulose minus the necessary catalysts. Thus, if celluloseacetate is to be made, the prehydrolysis bath will contain aceticanhydride and a solvent or diluent such as glacial acetic acid orbenzol.

After the prehydrolysis, the esterification process is initiated. Duringthe prehydrolysis, no cooling is necessary although it may be used. Themixture is then cooled to some extent to a temperature sufficiently lowso that the temperature during esterification does not exceed a certainmaximum, say 60 C. The esterifying catalysts, such as sulfuric acid, isthen added and the esterification process now proceeds. Due to the priortreatments, the cellulosic material is in a very reactive and uniformcondition, so that upon addition of the catalysts, a very smooth andquick reaction takes place. In the case of the acetylation of cellulose,the temperature rises in the course of 30 minutes from 8 or 10 C. toabout l2 to 45 C. At the peak temperature, the acetylation process ispractically completed. The reacting mass is then cooled and is thensubjected to the normal procedure of ripening, etc.

The process may be employed for preparing various organic esters ofcellulose such as cellulose acetate, cellulose formate, cellulosepropionate or cellulose butyrate. However, further details will be givenwith respect to the manufacture of cellulose acetate and the propertiesof cellulose acetate produced in accordance with our invention.

When yarns are made from ordinary cellulose acetate, the yarns orfabrics produced therefrom become delustered when subjected to theaction of boiling water or boiling dilute soap solutions. However, yarnsor fabrics made of cellulose acetate made in accordance with ourinvention are highly resistant to the action of boiling water or boilingsoap solutions, so that yarns or fabrics made of cellulose acetateprepared in accordance with our invention can be treated for a muchlonger time in such hot aqueous baths without losing their lusterappreciably. This property of resistance to delustering in boiling wateror soap solutions is of great benefit, for instance in the dyeing orcleaning of such yarns or fabrics.

To further illustrate our invention but without in any way being limitedt iereto, the following detailed description of one more of carrying outthe same is given:

Ewample The cellulosic material is first subjected to a pretreatmentprocess which comprises, for instance spraying 20 lbs. of glacial aceticacid The mixture is stirred in a wooden vessel of the horizontal typefor a period of time which may be up to three hours. lVhile thepretreatment is going on, the acetylizer proper is charged with 500 to600 lbs. say, 560 lbs. of a mixture of glacial acetic acid and aceticanhydride, the acetic anhydride comprising 38 to 39% of the mixture.This mixture of acetic anhydride and glacial acetic acid also containsabout 2 oz. of sulfuric acid. The mixture is then cooled to about 8 C. F

lfter pretreatment the cellulosic material is added to the acetylizercontaining the acetic acid and acetic anhydride. The temperature soonrises from about 8 to 15 (1, and as soon as the latter temperature isreached, 2 oz. of sodium carbonate are added to the mass. Stirring iscontinued for about an hour and then the temperature reduced to about 8C. This part of the process comprises the prehydrolysis treatment.

To cause acetylation, a mixture containing 13 to 16 lbs. say, lel lbs.of sulfuric acid and lbs. of a mixture of acetic anhydride and glacialacetic acid of the strength mentioned above, is now added. Thetemperature rises in the course of about 25 minutes to about 43 0.,which is the peak of the reaction. The acetylation reaction is nowpractically complete and there are practically no visible fibres in themass. The mass is then cooled down and ripened in any suitable manner tothe normal acetone soluble stage.

The term prehydrolysis fication and claims refers to the treatmentdescribed, and it is to be understood that the term does not necessarilymean that hydrolysis actually takes place in the treatment.

It is to be understood that the foregoing detailed description is givenmerely by way of illustration and that our invention is in nowiselimited thereto.

Having described our invention, what we claim and desire to secure byLetters Patent 1s:

1. In the method of making organic esters of cellulose, the steps ofsubjecting cellulose to pretreatment with a lower fatty acid and then toa pretreatment with an organic acid anhydride in the absenceofsutlicient catalyst to cause esterii'ication of the cellulose.

2. In the method of making cellulose acetat-e, the steps of subjectingcellulose to pretreatment with alower fatty acid and then to apretreatment with acetic anhydride and a liquid diluent in the absenceof sufficient catalyst to cause esterification of the cellulose. 3. Inthe method of making cellulose acetate, the steps of subjectingcellulose to pretreatment with acetic acid and then to a pretreatmentwith acetic anhydride and a liquid diluent in the absence of sufiicientcatalyst to cause esteriiication of the cellulose. I

4-. The method of preparing organic esters of cellulose comprisingsubjecting cellulose to pretreatment by agitating the same with arelatively small amount of a lower fatty acid, then prehydrolizing thecellulose by subjecting the cellulose to a bath containing used in thespeciacetic anhydride, which bath does not contain suflicient catalystto cause appreciable esterification, whereby prehydrolysis takes place,and then adding an esterification promoting catalyst to causeesterification.

5. lhe method of preparing cellulose acetate comprising subjectingcellulose to pretreatment by agitating the same with a relatively smallamount of a lower fatty acid, then prehydrolizing the cellulose bysubjecting the cellulose to a bath containing acetic anhydride, whichbath does not contain sufficient catalyst to cause appreciableacetylation, whereby prehydrolysis takes place, and then adding anacetylation promoting catalyst to cause acetylation.

6. Method of preparing cellulose acetate comprising subjecting celluloseto pretreatment by agitating the same witha relatively small amount ofacetic acid, then prehy drolizing the cellulose by subjecting thecellulose to a bath containing acetic anhydride, which bath does notcontain suflicient catalyst to cause appreciable acetylation, wherebyprehydrolysis takes place, and then adding an acetylation promotingcatalyst to cause acetylation.

7. Method of preparing cellulose acetate comprising subjecting celluloseto pretreatment by agitating the same with a relatively 8. Method ofmaking cellulose acetate of high clarity and/or deluster resistantproperties comprising mixing 100 parts of cotton linters withsubstantially 20 parts of glacial acetic acid, then mixing the mixturewith substantially 500 to 600 parts of a mixture containing glacialacetic acid and acetic anhydride and then adding from 13 to 16 parts ofsulfuric acid and substantially 100 parts of a mixture of glacial aceticacid and acetic anhydride.

9. A two-stage process of rendering cellulose more reactive towardsesterification, comprising first treating the same with an organic acidand then with organic acid anhydride in the absence of sufiicientcatalyst to cause esterification ofthe cellulose.

In testimony whereof, we have hereunto subscribed our names.

HERBERT E. MARTIN. JAMES \V. ELDER. LINWOOD N. ROGERS.

